1015. Reversible Primes (20)

1015. Reversible Primes (20)

A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (< 10⁵) and D (1 < D <= 10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:

The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:

For each test case, print in one line "Yes" if N is a reversible prime with radix D, or "No" if not.

Sample Input:

73 10
23 2
23 10
-2

Sample Output:

Yes
Yes
No

 

C++语言: Codee#22948

01 #include <cstdio>
02 #include <cmath>
03 #include <cstdlib>
04 #include <cstring>
05 #include <cctype>
06 #include <vector>
07 #include <map>
08 #include <queue>
09 #include <list>
10 #include <stack>
11 #include <bitset>
12 #include <set>
13 #include <fstream>
14 #include <sstream>
15 #include <iomanip>
16 #include <algorithm>
17 #include <iostream>
18
19 using namespace std;
20
21 FILE*            fin         = stdin;
22 FILE*            fout         = stdout;
23 const int        max_size     = 10086;
24
25 int is_prime(int x)
26 {
27     if(x == 2)
28         return 1;
29     if(x <= 1 || x % 2 == 0)
30         return 0;
31     int rg = sqrt((float)x) + 1;
32     for(int i = 3; i <= rg; i += 2)
33         if(x % i == 0)
34             return 0;
35     return 1;
36 }
37
38 int judge_reverse(int x, int rdx)
39 {
40     int rev = 0;
41     while(x)
42     {
43         rev = rev * rdx + x % rdx;
44         x = x / rdx;
45     }
46     return is_prime(rev);
47 }
48
49
50 int main()
51 {
52     int x, rdx;
53     while(scanf("%d", &x) && x >= 0)
54     {
55         scanf("%d", &rdx);
56         if(is_prime(x) && judge_reverse(x, rdx))
57             printf("%s\n", "Yes");
58         else
59             printf("%s\n", "No");
60     }
61
62     return 0;
63 }